After a two year absence, Spirit has won the right through the usual tedious political process to fly two daily roundtrips to Washington-National airport. It remains to be seen whether they will fly to Detroit or Ft. Lauderdale.
National airport, the preferred close-in airport for Washington, DC, has two levels of service limits placed on it: flights cannot exceed 1250 miles (with a few specifically-granted exceptions) and the number of flights or “slots” is strictly controlled.
The originally stated purpose of the 1250 mile limit, or “perimeter rule,” was to allow Washington-Dulles airport to build itself up as a base for long-haul flights. Ironically, by limiting the distance of flights at the close-in airport, National got more short flights and Dulles did not. So there wasn’t enough feeder traffic for long-haul flights, and the development of Dulles as a hub was hampered for a decade. The perimeter rule forced Dulles to more or less relies of the DC market for its flights instead of supplementing that traffic with connecting traffic.